Embryonic electrical connections appear to prefigure a behavioral circuit in the leech CNS |
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Authors: | Antonia Marin-Burgin F James Eisenhart William B Kristan Jr Kathleen A French |
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Institution: | (1) Section of Neurobiology, Division of Biological Sciences, University of California, 3119 Pacific Hall, San Diego, La Jolla, CA 92093-0357, USA;(2) Microsoft Research, 810 W. Emerson St., Seattle, WA 98119, USA |
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Abstract: | During development, many embryos show electrical coupling among neurons that is spatially and temporally regulated. For example,
in vertebrate embryos extensive dye coupling is seen during the period of circuit formation, suggesting that electrical connections
could prefigure circuits, but it has been difficult to identify which neuronal types are coupled. We have used the leech Hirudo medicinalis to follow the development of electrical connections within the circuit that produces local bending. This circuit consists
of three layers of neurons: four mechanosensory neurons (P cells), 17 identified interneurons, and approximately 24 excitatory
and inhibitory motor neurons. These neurons can be identified in embryos, and we followed the spatial and temporal dynamics
as specific connections developed. Injecting Neurobiotin into identified cells of the circuit revealed that electrical connections
were established within this circuit in a precise manner from the beginning. Connections first appeared between motor neurons;
mechanosensory neurons and interneurons started to connect at least a day later. This timing correlates with the development
of behaviors, so the pattern of emerging connectivity could explain the appearance first of spontaneous behaviors (driven
by a electrically coupled motor network) and then of evoked behaviors (when sensory neurons and interneurons are added to
the circuit). |
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Keywords: | Invertebrate Development Gap junction Behavior Neurobiotin |
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